Window and Door Flashing Best Practices

Windows represent one of the most vulnerable locations in the building envelope and the most common source of leaks.  Window and door flashings are designed to eliminate the risk of leaks and mold—which will also reduce your risk of call-backs.  We understand that there is an intimidating array of different types of flashing available, and many installation considerations. We wanted to share some practical information to help you understand the alternatives and best practices so you can choose and install wisely.

Types of Window and Door Flashing

Self-Adhesive Flashings (also called Peel ‘n Stick)

For light commercial and residential construction, self-adhesive flashings are the most popular option. When properly installed, they bond to the substrate and provide an effective seal against moisture.

Mechanically Applied Flashing

In some of the drier parts of the US, mechanically attached flashing continues to be preferred for its faster install and cost savings. It is affixed with fasteners directly to the substrate.

Fluid Applied Flashings

These flashing membranes are typically dispensed with a caulking gun from a tube or sausage and then troweled across the rough opening surface. The material provides complete coverage and is especially useful with intricate or complex install details.

Considerations

Temperamental

Just like kids, the adhesives used in self-adhesive flashings have their own personalities and unique behaviors. If you don’t pay attention they can misbehave and create all sorts of headaches.

Cold weather application: Many adhesives lose their grab as the installation temperature decreases. Use of a primer can improve adhesion in the cold. Pay attention to manufacturer specifications and be sure the primer you choose is compatible with the adhesive on the flashing. Always test before installing if they are not part of a proven system.

Heat build-up: If you have ever gotten into a closed car that has been sitting in the sun on a 100+ degree day, you already understand the concept of heat build-up.  There have been reports of cars reaching temperatures as high as 160° F. Wall assemblies are closed spaces, too, where the interior space can get much hotter than the ambient air temperature. A black wall with southern exposure in a heat-prone area like Phoenix can get just as hot—or hotter-- as the inside of that car. Some adhesives like asphalt can’t take that kind of heat, while high-performance adhesives like butyl and acrylic are better suited for high temperatures.

Material Compatibility: Some combinations of building materials do not play nice with each other and are incompatible. Check the manufacturer’s product information for any installation guidance or limitations. Make sure that the flashing is compatible with all the materials that it will contact. 

Seal the Deal

No matter what type of flashing you choose, you’ll need to use sealant (also known as caulk) with it.  This holds true even if the flashing is self-adhesive. Why? Sealant can fill in small voids in the substrate surface, ensuring a complete seal under the window flange without gaps. An elastomeric sealant will keep the window sealed during expansion and contraction due to temperature changes. While it may not be required by all code bodies, it is a definite best practice around windows.

The other best practice, required by nearly all manufacturers, is the use of a J-roller to press the flashing down. This practice eliminates air gaps and ensures a tight bond between the flashing adhesive and the substrate. Many adhesives are also pressure-sensitive and require rolling to activate the adhesive. Those short few minutes you take to J-roll that flashing can save you hours of call-back time.

Mind the Method

The sequencing of weatherization materials is critical to successful moisture management. There are several methods of window installation and weatherization approved by AAMA (American Architectural Manufacturers Association). They are conveniently denoted by letter. These methods have been developed and standardized based on years of field experience.  When you follow a standardized method, you can be confident that it will be leak-free.

You can find more information here:  

• Method A Download
• Method A Video
• Method A1 Download
• Method A1 Video
• Method B Download
• Method B Video

Other Uses

Self-adhesive flashing tape is also often called on to seal other vulnerable parts of the structure. It can be used to seal around other penetrations like electrical boxes and can provide critical waterproofing on small, non-roof structures such as pot shelves and parapets. It can be used to easily create sill pans (watch here). It is also used to reinforce the interior and exterior corners of the building envelope.

The Bottom Line